Final answer:
The oxidation of a lipid molecule is an example of a spontaneous reaction, as it occurs naturally without continuous energy input and moves the system to a more stable state.
Step-by-step explanation:
In the context of spontaneous reactions with lipids, the key factor to consider is whether the reaction occurs naturally and without the constant input of external energy. A spontaneous reaction is one that has a natural tendency to occur, releasing free energy and moving towards a more stable state. Considering the choices provided:
- Hydrolysis of a lipid molecule
- Synthesis of a lipid molecule
- Oxidation of a lipid molecule
- Reduction of a lipid molecule
The example of a spontaneous reaction with lipids is the oxidation of a lipid molecule. Oxidation reactions, such as the oxidation of plastics and iron rusting in a moist atmosphere, occur naturally and spontaneously without the need for continuous energy input. Moreover, while the oxidation reaction may occur slowly, it still progresses without the need for external energy, hence it is spontaneous. In contrast, biosynthetic processes like the synthesis and reduction of lipids normally require energy input and are therefore nonspontaneous.